Genetics 5th Edition by Leland Hartwell ,Michael Goldberg,Janice Fischer ,Leroy Hood,Charles Aquadro

Exercise 6

The general protocol for using the chi-square test for goodness of fit and evaluating its results can be stated in a series of steps. Two preparatory steps precede the actual chi-square calculation.
Table 5.2 Critical Chi-Square Values
Evaluate the significance of the p value. You can think of the p value as the probability that the null hypothesis is true. A value greater than 0.05 indicates that in more than 1 in 20 (or more than 5%) repetitions of an experiment of the same size, the observed deviation from predicted values could have been obtained by chance, even if the null hypothesis is actually true; the data are therefore not significant for rejecting the null hypothesis. Statisticians have arbitrarily selected the 0.05 p value as the boundary between rejecting or not rejecting the null hypothesis. A p value of less than 0.05 means that you can consider the deviation to be significant, and you can reject the null hypothesis.